Attempts have been made in the past to combine use of a cryogenic freezing process prior to mechanical refrigeration to freeze food products. The so called hybrid systems boost overall production, reduce dehydration to some extent, but increase the freezing costs. In order to use a hybrid system attempts have been made to utilize the vaporizing cryogen in the mechanical refrigeration system to enhance the mechanical refrigerator. U.S. Pat. Nos. 4,856,285 and 4,858,445 disclose and claim devices to utilize vaporized cryogen by heat exchanging the vaporizing cryogen against the atmosphere in the mechanical refrigeration unit by means of a separate heat exchanger. Such devices require extensive equipment and the heat transfer is not as effective as could be accomplished with a direct heat exchange.